In recent years, the market of consumer electronic products and LED driving circuits grows constantly and power converters come with a power saving function and a smaller size, so that related electrical and electronic devices usually adopt a conventional AC/DC converter which is also known as a peak rectifier and composed of four diodes and output capacitors. Such converter has the advantages of low cost and stable circuit and the disadvantages of low power factor and high harmonics.
As to electric power, an increase of power factor (PF) also increases the consumption the electric power, and a common solution is to install a power factor correction (PFC) device with a typical pulse width modulation (PWM) circuit (as shown in FIG. 1) to increase the power factor up to a range of 0.98˜0.99. However, the whole system of this solution has the drawbacks of a large volume and a high cost and results in a limited application of compact electronic products.
Therefore, another passive power factor control technology adopting a passive component is provided to improve the power factor (PF) and a total harmonic distortion (THD) such as a valley fill circuit as shown FIG. 2. In general, the performance of the passive power factor control technology is very low and can barely meet the requirement or lower limit of an acceptable range of industrial standards.
As the development of green energies becomes a global issue, and the efficiency of electric power is taken seriously, semiconductor controlled power integrated circuits (IC) play an important role of enhancing the efficiency of the electric power, and the power IC control technology can save total cost and reduce unnecessary switching loss. This technology mainly uses a pulse DC signal with a positive half-cycle sinus waveform to modulate the width of duty cycle, so that a load can be operated continuously in a complete sinus waveform. However, the conventional power factor improvement circuit with the sinus waveform is simply used in the pulse DC signal with the positive half-cycle sinus waveform to modulate the pulse width of the duty cycle, and thus still causes a low efficiency of the circuit. Up to now, there is still no design available to improve the performance in order to control the power factor to a level over 0.90 when a full voltage of 90˜264V is inputted.